Lanthanide-Doped Nanomaterials as Potential Bioprobes

The remarkable optomagnetic properties of the lanthanides (Ln) make Ln-based materials ideal for biomedical applications, including diagnostic (for instance, imaging or thermal sensing) and therapeutic (for instance, drug delivery and photodynamic therapy) approaches. This is due the unique electronic properties of the Ln (f-elements) allowing for upconversion and near-infrared emission under near-infrared excitation as well as high magnetic moments.<br/>Sodium lanthanide fluorides (NaLnF₄) are our favorite materials, and we developed a fast and reliable microwave-assisted synthetic approach allowing crystalline phase and size control in the sub 15 nm realm. Such control is crucial for the understanding of fundamental structure-property relationships and to optimize their optical and magnetic properties, when aiming for the design of next-generation optical probes or contrast agents for magnetic resonance imaging (MRI). For instance, NaGdF₄ nanoparticles (NPs) are gaining interest as alternative MRI contrast agent, while co-doping with emitting Ln³⁺ ions endows the NPs with luminescent properties for applications as optical probes. The hexagonal crystalline phase of NaGdF₄ is known as the more efficient host material for upconversion emission (i.e., the emission of one higher energy photon following excitation with two or more lower energy photons). In contrast, we observed that the cubic phase of NaGdF₄ shows superior performance as MRI contrast agent.<br/>Having a fast and reliable synthetic route towards NaLnF₄ NPs on hand, we now explore various nanoparticle architectures and compositions with the goal to optimize their optomagnetic properties, ultimately resulting in the design of biocompatible multimodal bioprobes. This includes MRI contrast agents based on Gd- and Dy-containing NPs, and novel near-infrared emitters based on Ho or Pr for deep tissue optical bioimaging under near-infrared illumination, matching the biological transparency windows. In this presentation, we will also have a look at luminescent NaLnF₄ NPs with various surface-modifications and the suitability of hyperspectral imaging to study their nano-bio interactions.